In order to manufacture a semiconductor integrated circuit, various processes such as film forming, etching, oxidation and diffusion are performed on a wafer. In such processes, a throughput and a yield are required to be improved along with the trend of miniaturization and high integration of the semiconductor integrated circuit. From this point of view, a semiconductor processing system known as a so-called cluster tool has been developed, wherein a plurality of processing apparatuses performing a same process or a plural number of processing apparatuses performing different processes are connected with one another via a common transfer chamber such that various processes can be successively executed without exposing a wafer to the atmosphere. A cluster tool type semiconductor processing system is disclosed in, e.g., Japanese Patent Laid-open Publication Nos. 2000-208589 and 2000-299367.
As for such a processing system, there is a type in which a port structure for mounting a cassette with semiconductor wafers is disposed at a front end thereof. A wafer in the cassette is carried into the system by a transfer arm and then loaded into a load-lock chamber capable of controlling a pressure to be set at a level between the vacuum and the atmospheric pressure. Next, the wafer is loaded into a common vacuum transfer chamber whose peripheral portions are connected to a plurality of vacuum processing apparatuses and then sequentially loaded into each of the vacuum processing apparatuses surrounding the common transfer chamber located at the center to thereby undergo continuous processes. Further, a processed wafer returns to a primary cassette along, e.g., a primary path.
In general, in a facility in which a semiconductor processing system is installed, an atmosphere of clean air is maintained at a predetermined level of cleanliness. Further, in the processing system, a chamber into which the wafer is introduced maintains an atmosphere of clean air at a higher level of cleanliness in order to more completely prevent particles from being introduced into a succeeding load-lock chamber and the like.
A cassette itself has a closed structure or an open structure depending on a wafer size. For example, in case of a cassette for 300 mm wafers, the cassette itself has a closed structure (closed type cassette). In such case, when the wafer is loaded thereinto, a cover of an opening of the cassette is removed, and an operation is performed while keeping the opening close to a port of the processing system (see, e.g., Japanese Patent Laid-open Application No. 1999-145245). Accordingly, a highly stable loading operation can be performed.
Meanwhile, in case of a cassette for, e.g., 200 mm wafers, the cassette itself has an open structure (open type cassette). In this case, it is preferable to separate the cassette from an operator in order to perform the loading operation safely.